Impacts of bladder and rectum filling status on their dosimetric parameters in helical tomotherapy for cervical cancer / 中华放射肿瘤学杂志

ABSTRACT

Objective To analyze the changes in volume and the planning volume of the bladder and rectum during helical tomotherapy (HT) treatment for cervical cancer,and to evaluate the impacts of bladder and rectum filling on their dosimetric parameters.Methods Twenty patients with cervical cancer who received HT in our hospital from 2012 to 2016 were enrolled as subjects.Before treatment,megavolt computed tomography (MVCT) and registration of planning CT images were preformed to recalculate the dose distribution,delineate the target volume,and measure the volume and position of the bladder and the rectum.Each MVCT image and the corresponding single dose were obtained by dose reconstruction using the Planned Adaptive module in HT planning workstation.The fused MVCT images and the corresponding single dose for each MVCT were loaded to MIM Maestro software 6.0 for dose stacking.The obtained total radiation dose was compared with that obtained by kilovolt CT.Between-group comparison was made by paired t-test or analysis of variance.Results If the volume change in the bladder was more than 400 ml or the rate of volume change was higher than 60％,the displacements of the bladder centroid toward the foot and dorsal sides were significantly increased;the Dmean and V50 were significantly increased (P＜0.05).If the volume change in the rectum was more than 30 ml or the rate of volume change was higher than 30％,the displacements of the rectum centroid toward the head and ventral sides were significantly increased;the V45 and V50 for the rectum were significantly increased (P＜0.05).Conclusions Although the bladder filling status has little effect on the radiation dose to the bladder,the volume change or the rate of volume change should be no more than 400 ml or 60％,respectively.Moderately filled bladder is recommended for positioning and treatment,which achieves satisfactory repeatability of the treatment.A volume change of more than 30 ml or a rate of volume change of higher than 30％ can result in an increase in the dose to the rectum.Empty rectum can effectively reduce the dose to the rectum.